We have the tag obscure-terms. It has 36 questions and the only thing obscure about them is the thought process that lead people to tag them with this tag. Mostly words that seemed obscure to the OPs, sometimes regarding the actual word obscure, sometimes completely arbitrary.

I don't think there is a proper tag this tag can be made synonym of. I think we should start with gradually re-tagging the questions manually.

Does it describe the contents of the questions to which it is applied? and is it unambiguous?

Hell no! The questions are an arbitrary bunch only kept together by tag.

Is the concept described even on-topic for the site?

If there were a discernible concept, maybe. The tag has no information and googling and meta dictionaries like onelook.com cannot provide any information about obscure terms being an established concept of any sort.

Does the tag add any meaningful information to the post?

It certainly does not seem so. There are also no followers of the tag. The tag is completely arbitrarily used.

Does it mean the same thing in all common contexts?

Certainly not. They range from concerning the words obscure to regarding more or less uncommon words.